DRAINED SHEAR STRENGTH OF COMPACTED KHON KAEN LOESS FROM MULTISTAGE TRIAXIAL TEST

The previous research found that Khon Kaen loess is collapsible soil. The structure of Khon Kaen loess is a honeycomb structure and loose adhesion. The cause of losing shear strength and collapsing is the increase in moisture content. The purpose of this study was to investigate the influence of matric suction on the shear strength of compacted Khon Kaen loess by a multistage consolidated drained triaxial test. According to the soil water characteristic curve, the matric suction of this study consists of saturation regime at matric suction of 0 kPa, transition regime at matric suction of 10 kPa, and the residual regime at matric suction of 50 kPa and 100 kPa. The testing result indicated that the cohesion intercept (c) is non-linearly increasing with matric suction. The effective friction angle (φ′) is also increasing with matric suction. However, the angle with respect to changes in matric suction (φb) is gradually decreasing. According to the test result, the active earth force (Pa) decreases with increasing matric suction. However, the bearing capacity was increased with increasing matric suction. Therefore, the matric suction influences the size of the cantilever wall. In conclusion, this research shows that matric suction influences the shear strength of Khon Kaen loess. Furthermore, the unsaturated shear strength is useful and alternative to foundation design because the width of the foundation is not excessive, saving material costs.